North Korea lost contact with one of its submarines earlier this week, three U.S. officials familiar with the matter told CNN Friday. The U.S. is unsure whether the missing vessel is adrift at sea or has sunk, officials said. 

The U.S. military had been watching the submarine operate off North Korea’s east coast when the vessel stopped. For days, the U.S. military has been secretly watching the North Korean navy search for the submarine, CNN reported. 



Last week, North Korea fired two short-range ballistic missiles into the sea, according to the South Korean military. The move came amid growing tensions in the rogue country, as North Korea views the U.S. and South Korea's annual military drills as a rehearsal for a possible invasion. In January, North Korea conducted its fourth nuclear test, drawing global condemnation and earning the country new sanctions from the United Nations.